scholarly journals EQUILIBRIUM PROFILES AND LONGSHORE TRANSPORT OF COARSE MATERIAL UNDER OBLIQUE WAVE ATTACK

1976 ◽  
Vol 1 (15) ◽  
pp. 73 ◽  
Author(s):  
E. Van Hijum
Keyword(s):  
Research Programme ◽  
Design Criteria ◽  
Regular Wave ◽  
Oblique Wave ◽  
Wave Approach ◽  
Longshore Transport ◽  
Equilibrium Profiles ◽  
Equilibrium Profile ◽  
Gravel Beaches ◽  
Profile Characteristics

In order to obtain design criteria for artificial gravel beaches, a research programme was drawn up to study the behaviour of gravel beaches under wave attack. The present paper gives the main results of the investigations into beach formation and equilibrium profile characteristics, including the longshore transport rate of beach material under regular wave attack with varying angles of wave approach,

scholarly journals EQUILIBRIUM PROFILES OF COARSE MATERIAL UNDER WAVE ATTACK

1974 ◽  
Vol 1 (14) ◽  
pp. 54 ◽  
Author(s):  
E. Van Hijum
Keyword(s):  
Research Programme ◽  
Design Criteria ◽  
Coarse Material ◽  
Equilibrium Profiles ◽  
Equilibrium Profile ◽  
Gravel Beaches

In order to obtain design criteria for artificial gravel beaches, a research programme was drawn up to study the behaviour of gravel beaches under wave attack. The present paper gives the main results of the first step in this programme, viz. the determination of the dimensions, form and way of formation of an equilibrium profile under regular, perpendicular wave attack. One of the conclusions is that gravel with a D0(,

Equilibrium Profile of Modern Belted Radial Ply Tires: Its Determination and Performance Benefits

2013 ◽  
Vol 41 (2) ◽  
pp. 127-151
Author(s):  
Rudolf F. Bauer
Keyword(s):  
Finite Element ◽  
Aspect Ratio ◽  
Finite Element Methods ◽  
Mathematical Analysis ◽  
Internal Stresses ◽  
Stress Concentrations ◽  
Equilibrium Profiles ◽  
Equilibrium Profile ◽  
And Performance ◽  
Beneficial Property

ABSTRACT The benefits of a tire's equilibrium profile have been suggested by several authors in the published literature, and mathematical procedures were developed that represented well the behavior of bias ply tires. However, for modern belted radial ply tires, and particularly those with a lower aspect ratio, the tire constructions are much more complicated and pose new problems for a mathematical analysis. Solutions to these problems are presented in this paper, and for a modern radial touring tire the equilibrium profile was calculated together with the mold profile to produce such tires. Some construction modifications were then applied to these tires to render their profiles “nonequilibrium.” Finite element methods were used to analyze for stress concentrations and deformations within all tires that did or did not conform to equilibrium profiles. Finally, tires were built and tested to verify the predictions of these analyses. From the analysis of internal stresses and deformations on inflation and loading and from the actual tire tests, the superior durability of tires with an equilibrium profile was established, and hence it is concluded that an equilibrium profile is a beneficial property of modern belted radial ply tires.

SOME FEATURES OF THE EQUILIBRIUM COASTAL PROFILE FOR DIFFERENT INITIAL BED SLOPES BASED ON MODELLING STUDY

2017 ◽  
Author(s):  
Dmitry Korzinin ◽  
Dmitry Korzinin ◽  
Igor Leontiev ◽  
Igor Leontiev
Keyword(s):  
Time Scales ◽  
Wave Impact ◽  
Grain Sizes ◽  
Equilibrium Profiles ◽  
Equilibrium Profile ◽  
The Mean ◽  
Wave Conditions ◽  
Bed Slope ◽  
Coastal Profile ◽  
Modelling Study

Modelling study of the equilibrium profiles formed on sandy coasts of different bed slopes and grain sizes under the various wave conditions was realized by using the CROSS-P and Xbeach morphodynamic models. A special criterion taking into account a total volume of bed deformations per one hour was suggested to determine the conditions of profile stabilization. For both models the time scales of equilibrium profile formation were found to be the same. However, the deformation magnitudes differed significantly. Bed deformations were computed on the whole profile length over the 200-hours duration of wave impact. It was concluded that both models predict a trend of the bed slope toward a stable value. CROSS-P model shows the widening of accumulative terrace during the profile evolution. The mean slope of the equilibrium profile was found to depend on the initial bed slope.

Wave Run-Up at Sea Dikes under Oblique Wave Approach

1982 ◽  
Author(s):  
E. Tautenhain ◽  
S. Kohlhase ◽  
H. W. Partenscky
Keyword(s):  
Oblique Wave ◽  
Wave Approach ◽  
Run Up ◽  
Sea Dikes

Drilling Riser Disconnection Challenges in Ultra-Deep Water

2018 ◽  
Author(s):  
Alexandre Diezel ◽  
Germain Venero ◽  
Victor Gomes ◽  
Leandro Muniz ◽  
Rafael Fachini ◽  
...  
Keyword(s):  
Good Representation ◽  
Regular Wave ◽  
Computational Simulations ◽  
Successful Operation ◽  
Dynamic Positioning System ◽  
Drilling Rig ◽  
Wave Approach ◽  
Short Period ◽  
Drilling Operations ◽  
The Time Domain

With the extension of the offshore drilling operations to water depths of 10,000 ft and beyond, the technical challenges involved also increased considerably. In this context, the management of the riser integrity through the application of computational simulations is capital to a safe and successful operation — particularly in harsh environments. One of the main challenges associated with keeping the system under safe limits is the recoil behavior in case of a disconnection from the well. The risk that an emergency disconnect procedure can take place during the campaign is imminent, either due to failure of the dynamic positioning system or due to extreme weather in such environments. Recent work [1] in the field of drilling riser dynamic analysis has shown that the recoil behavior of the riser after a disconnection from the bottom can be one of the main drivers of the level of top tension applied. Tension fluctuations can be very large as the vessel heaves, especially in ultra-deep waters where the average level of top tension is already very high. In order to be successful, a safe disconnection must ensure that the applied top tension is sufficient for the Lower Marine Riser Package (LMRP) to lift over the Blow-Out Preventer (BOP) with no risk of interference between the two. This tension should also not exceed a range in which the riser will not buckle due to its own recoil, that the telescopic joint will not collapse and transfer undesirable loads onto the drilling rig or that the tensioning lines will not compress. A good representation of such behavior in computational simulations is therefore very relevant to planning of the drilling campaign. A case study is presented herein, in which a recoil analysis was performed for a water depth of 11,483ft (3,500m). Numerical simulations using a finite element based methodology are applied for solving the transient problem of the riser disconnection in the time domain using a regular wave approach. A detailed hydro-pneumatic tensioning system model is incorporated to properly capture the effect of the anti-recoil valve closure and tension variations relevant during the disconnection. A reduction of conservativism is applied for the regular wave approach, where the maximum vessel heave likely to happen in every 50 waves is applied instead of the usual maximum in 1000 waves approach. ISO/TR 13624-2 [4] states that using the most probable maximum heave in 1000 waves is considered very conservative, as the event of the disconnection takes place in a very short period of time. The challenges inherent to such an extreme site are presented and conclusions are drawn on the influence of the overall level of top tension in the recoil behavior.

scholarly journals WAVE RUN-UP AT SEA DIKES UNDER OBLIQUE WAVE APPROACH

1982 ◽  
Vol 1 (18) ◽  
pp. 50
Author(s):  
E. Tautenhain ◽  
S. Kohlhase ◽  
H.W. Partenscky
Keyword(s):  
Irregular Waves ◽  
Wave Direction ◽  
Wave Runup ◽  
Natural Conditions ◽  
Wave Impact ◽  
Oblique Wave ◽  
Wave Flume ◽  
Wave Approach ◽  
Impact Forces ◽  
Run Up

Besides wave impact forces, erosion of the inner side of a sea dike is a serious cause of destruction. Therefore, wave run-up and overtopping effects have to be considered with respect to the safety of a dike. Strong relations were found between both these influences (TAUTENHAIN et.al., 1980, 1981, 1982), based on experiments in a wave flume and using an energy conservation concept. However, under natural conditions, an oblique wave approach has to be considered. This paper deals with the influence of wave direction on wave runup on a smooth dike slope in order to provide a basis for calculating the overtopping rates for both regular and irregular waves.

Irregular Wave Simulation and Fatigue Damage Evaluation of a Flexible Riser Subjected to Bi-Modal Sea States

2012 ◽  
Author(s):  
Zhimin Tan ◽  
Yucheng Hou ◽  
John Zhang ◽  
Terry Sheldrake
Keyword(s):  
Fatigue Damage ◽  
Wave Train ◽  
Time History ◽  
Regular Wave ◽  
Flexible Riser ◽  
Single Wave ◽  
Irregular Wave ◽  
Wave Approach ◽  
Wave Simulation ◽  
Wind Sea

This paper presents the fatigue evaluation of a flexible riser subjected to bi-modal sea states, where the local wind and swell conditions act simultaneously, and is observed in many offshore regions including Brazil and West Africa. Due to the irregularity of the riser responses, the traditional, regular wave approach for assessing the fatigue damage of a flexible pipe cannot be applied without significant simplifications. A typical deviation would be to treat the combined swell and wind conditions at sea as two sets of separate cases. The regular wave approach can then be applied and the summation of the damage of both cases defined as the final damage of the pipe. As an alternative, this paper presents a more theoretically accurate irregular wave approach. The entire irregular wave simulation was first performed using the commercial software, OrcaFlex™, together with a tensile wire stress model developed in-house. The model implements the pipe bending hysteresis behavior during dynamic excitation, producing corresponding time history stress results, which are used to assess the fatigue damage using a rain-flow counting method. Two case studies are presented, the first being a dynamic simulation performed with two wave trains generated based respectively on the given swell and wind sea spectrums. In the second case study, a single wave train is generated based on the combined spectrum of the swell and wind sea states. Both results are compared with those obtained by the traditional regular wave approach and a preferred analysis method is recommended based on the conservatism and time efficiency.

Improving Operating Window for Disconnect Operations of CWO Risers

2010 ◽  
Author(s):  
Guttorm Gryto̸yr
Keyword(s):  
Rigid Body ◽  
Wave Height ◽  
Irregular Waves ◽  
Regular Wave ◽  
Irregular Wave ◽  
Wave Approach ◽  
Tension Level ◽  
Rigid Body Model ◽  
Industry Practice ◽  
Operating Window

The term ‘riser recoil’ refers to the situation when the lower end of a top tensioned riser is released, and the riser is lifted up by the riser tensioner and/or top motion compensator system on the supporting vessel. The elastic energy stored in the riser is then released, and the riser ‘recoils’. This paper focuses on the case of planned disconnect, and builds on ref. [1] which was based on a simplified riser analysis using a rigid body to represent the riser. In the present paper, the methodology has been applied to an elastic riser model in the riser analysis software RIFLEX, from MARINTEK in Trondheim, Norway, which includes axial damping elements required for modeling of the tensioner systems. Completion and Work Over (CWO) risers are unique in the sense that they may be simultaneously connected to both the riser tensioner system and the top motion compensator system of a drilling vessel. A Marine Drilling riser, on the other hand, is only connected to the riser tensioner system. Typically the riser tensioner system has a stroke of ± 8–9 m, whereas the top motion compensator system has only ± 3.5–4 m. It is imperative that the connector is lifted clear of the subsea structure in order to avoid damage to the equipment after the riser has been disconnected. The operating window for planned disconnect of CWO risers is severely limited by the available stroke of the top motion compensator. One of the purposes of the disconnect analysis is to establish the maximum wave height at which there is still sufficient clearance between the connector and the subsea structure after disconnect. Previous experience has shown that this may be the governing limitation for workover operations. The analysis may also establish a maximum tension level, and seastate, to avoid hard stroke-out of the top motion compensator cylinders. This requires an elastic riser model, since a rigid body will yield unphysically large impulse loads in case of stroke-out. The current industry practice is to use a regular wave approach in the analysis. In accordance with ref. [1], the present analysis is performed with irregular wave analyses. The results are documented through a case study of a typical CWO riser system connected to a semi-submersible in typical North Sea environmental conditions. The semi-submersible and the CWO riser system are exposed to irregular waves. Comparison of the resulting allowable wave height shows that using the approach presented here with an elastic riser model yields less conservative results than the previous methodology with a rigid body model. This should be coupled to the findings with the rigid riser model, ref. [1], that irregular waves yield a considerable increase in the operating window, and the resulting operability, compared to a regular wave analysis. Hence, using a regular wave approach combined with a simplified riser model that neglects the flexibility of the riser is expected to yield overly conservative results for the EQDP elevation after disconnect.

scholarly journals CARIBBEAN BEACH-FACE SLOPES AND BEACH EQUILIBRIUM PROFILES

1988 ◽  
Vol 1 (21) ◽  
pp. 120 ◽  
Author(s):  
John D. Boon ◽  
Malcolm O. Green
Keyword(s):  
Objective Measure ◽  
Field Measurements ◽  
The United States ◽  
Gravitational Acceleration ◽  
Sediment Grain Size ◽  
Practical Result ◽  
Average Value ◽  
Caribbean Islands ◽  
Equilibrium Profiles ◽  
Equilibrium Profile

Field measurements performed on two Caribbean islands revealed that two-dimensional nearshore bottom morphology is well represented by Dean's (1977) model of the beach equilibrium profile, h - A xm, where h is depth below mean water level at a distance x offshore and A is a scale factor. For the curvature, m, we obtained an average value of approximately m - 1/2 through least squares curve fitting of observed profile data, yielding a more concave and therefore steeper profile inshore than m — 2/3, the average previously reported by Dean for quartz sand beaches in the United States. Furthermore, an objective measure of beach steepness was found to be A-*-'1", a quantity which utilizes both of Dean's parameters and which may serve as a surrogate for the beach-face slope, tan /3, on highly concave beaches. Reasonable correlations were found between A?-'m and the environmental parameter, H^ /gDT , where H^ is breaker height, D is sediment grain size, T is wave period and g is gravitational acceleration. Improved prediction of Caribbean beach slopes and beach equilibrium profiles is an important practical result.

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